A cellular communication system projects a number of "beams" or "cells" over the earth. A communication unit (CU) communicates within a cell containing multiple channels. Channel access is allocated by frequency, time, by coding, or by a combination of frequency, time, and/or coding to the cells of the system such that communications occurring in adjacent cells use different channels to minimize the likelihood of interference between channels. Over a large pattern of cells, channels can be reused repeatedly by distributing common channels over the entire cell pattern such that only non-adjacent cells reuse the same channels.
A non-geostationary orbit (NGSO) mobile satellite system employing satellite-fixed cells must address the motion of satellite antenna cell coverage areas relative to the CUs. In this context, a "cell" or "beam" is defined as the coverage area formed on the earth's surface by a single antenna beam, and a satellite "footprint" is defined as the aggregation of all cells or beams formed by the antennas of a single satellite. Satellite cells sweep over the earth's surface at such a high rate of speed that a given CU is moved through a number of beams or cells during the course of a particular communication. Frequently, a CU could be serviced not only by multiple cells or beams of a single satellite, but also by two or more different satellites during the course of the communication.
As a satellite moves in its orbit, it becomes necessary to hand-off communications or traffic with each CU in a first cell to different cells within a satellite footprint and ultimately to cells of a footprint of an adjacent satellite. In prior art systems, individual CUs generally are handed-off individually requiring at least two messages for handing-off each CU, one for the CU to request to be handed-off, and a second for the satellite to grant the hand-off. The need for processing multiple messages from multiple CUs during hand-offs consumes substantial amounts of bandwidth and satellite processing power in the satellite communication system.
Thus, what is needed is a method and apparatus to control CU hand-offs of communications or traffic in a NGSO satellite communication system without consuming substantial amounts of bandwidth and/or satellite processing power.